Combination gas/oil burner

ABSTRACT

A burner suitable for firing a gaseous fuel, or a combination of a gaseous and a liquid fuel, with the gas being used to atomize the liquid fuel. The burner includes an inner liquid fuel tube which is surrounded by a primary gas tube that is positioned within a secondary gas tube. The liquid fuel tube is connected to a source of liquid fuel and at its outer end has a nozzle with several discharge orifices. The primary and secondary gas tubes are each connected to a source of gaseous fuel and each has a discharge opening at its outer end. The secondary gas tube discharge opening is of annular shape and surrounds the discharge opening of the primary gas tube. The liquid fuel tube nozzle defines a constricted discharge passage with the primary gas tube discharge opening. Liquid fuel passing into this passage from the liquid fuel tube nozzle is atomized by primary gas which also passes through the passage, and the atomized liquid fuel and primary gas pass from the burner through the discharge opening at the outer end of the primary gas tube. Secondary gas discharged from the secondary gas tube discharge opening impinges on the liquid fuel primary gas mixture discharged from the discharged opening of the primary gas tube. A pressure regulator maintains constant the pressure of the primary gas passing into the primary gas tube, over the range of total gas flow rates, assuring adequate primary gas pressure and flow for atomization of the liquid fuel, even at low total gas flow rates. The burner has given excellent results in atomizing fuel oil with gas flows as low as 15 percent of the B.t.u. fired at a high firing rate (30 g.p.h. oil equivalent total fuel in the case of the burner tested) and also with 50 percent gas at a low firing rate (10 g.p.h. equivalent total fuel.

United States Patent [72] Inventors Allentown; Eugene M. Rudzki, Bethlehem, both of Pa. [211 App]. No. 46,710 [22] Filed June 16, 1970 [45] Patented Oct. 5, 1971 [73] Assignee Bethlehem Steel Corporation [54] COMBINATION GAS/OIL BURNER 1 Claim, 3 Drawing Figs.

[52] US. Cl 239/412, 239/419.3, 239/417.5 [51] Int. Cl B05b 7/12 [50] Field of Search 239/412, 413, 416.1, 417.5, 419.3, 422, 423, 424.5, 427.5

[56] References Cited UNITED STATES PATENTS 801,360 10/1905 Christensen 239/412 1,071,381 8/1913 Anthony 239/422 X 1,234,088 7/1917 Ralston 239/427.S 1,737,945 12/1929 Rigby 239/427.5 X 2,368,178 1/1945 Turpin.... 239/458 X 3,408,985 11/1968 Sedlacsik 239/4175 X FOREIGN PATENTS 1,381,566 11/1964 France 239/413 6,609,443 8/1967 Netherlands 239/422 Bradford K. Pea se Primary ExaminerM. Henson Wood, J r. Assistant Examiner-Edwin D. Grant Attorney-James T. Seavey ABSTRACT: A burner suitable for firing a gaseous fuel, or a combination of a gaseous and a liquid fuel, with the gas being used to atomize the liquid fuel. The burner includes an inner liquid fuel tube which is surrounded by a primary gas tube that is positioned within a secondary gas tube. The liquid fuel tube is connected to a source of liquid fuel and at its outer end has a nozzle with several discharge orifices. The primary and secondary gas tubes are each connected to a source of gaseous fuel and each has a discharge opening at its outer end. The secondary gas tube discharge opening is of annular shape and surrounds the discharge opening of the primary gas tube. The liquid fuel tube nozzle defines a constricted discharge passage with the primary gas tube discharge opening. Liquid fuel passing into this passage from the liquid fuel tube nozzle is atomized by primary gas which also passes through the passage, andthe atomized liquid fuel and primary gas pass from the burner through the discharge opening at the outer end of the primary gas tube. Secondary gas discharged from the secondary gas tube discharge opening impinges on the liquid fuel primary gas mixture discharged from the discharged opening of the primary gas tube. A pressure regulator maintains constant the pressure of the primary gas passing into the primary gas tube, over the range of total gas flow rates, assuring adequate primary gas pressure and flow for atomization of the liquid fuel, even at low total gas flow rates. The burner has given excellent results in atomizing fuel oil with gas flows as low as 15 percent of the B.t.u. fired at a high firing rate g.p.h. oil equivalent total fuel in the case of the burner tested) and also with percent gas at a low firing rate (10 g.p.h. equivalent total fuel.)

COMBINATION GAS/OIL BURNER BACKGROUND OF THE INVENTION The field of art to which the invention pertains is that of a high-temperature combination gas/oil burner with good atomization of the liquid fuel by the gas over a broad range of firing rates and gas/oil ratios.

SUMMARY OF THE INVENTION When a liquid fuel such as No. 6 fuel oil is fired in a furnace, the oil, prior to combustion, must be atomized into fine droplets by some effective atomizing medium. In industrial furnaces, steam and air are widely used for atomization of liquid fuels. However, steam and compressed air are costly and make no significant thermal contribution to the flame. Furthermore, steam or air will tend to create undesired scale on heated ferrous metals, and also to have a decarburizing effect thereon. In contrast, gaseous fuel, e.g., natural gas, with its high calorific value, is an ideal medium for atomizing liquid fuel, provided that the gas pressure can be kept sufficiently high and constant for efficient atomization over a wide range of burner firing rates.

The present burner uses natural gas to atomize No. 6 fuel oil, but will give good performance with any gaseous fuel as an atomizing agent and virtually any atomized liquid fuel, including preheated tar or pitch. This combination gas/oil burner has proven capable of firing, on a B.t.u. basis, either 100 percent gas or up to 85 percent oil with a minimum of 15 percent gas required for atomization of the oil. The range of firing rates for the burner tested was to 30 g.p.h. oil (720 to 4,300 s.c.f.h. natural gas); however, this burner design is adaptable to burners of any industrial capacity.

It is an object of the present invention to provide an improved liquid/gaseous fuel burner which automatically maintains constant gas pressure required for good atomization of the liquid fuel. I

Another object of the invention is to provide a burner which can fire gas over a wide range of rates above the minimum required for atomization of the liquid fuel.

Particular features of the present burner are:

I. Introduction of primary gas to a liquid-fuel atomizer having passages which pass only a primary fraction of the total gas flow to the burner.

2. lmpingement of the secondary gas, discharging from a fixed annulus, on the primary gas-oil mixture.

3. Use of the back-pressure regulator valve in the secondary gas line to maintain constant primary gas pressure at all gas total flow rates.

For brevity in this specification, it will be understood that the term oil" where used hereinafter is intended to include all ordinary forms of liquid fuels, and that the term gas similarly includes both natural and artificial combustible gases.

DESCRIPTION OF THE DRAWINGS In the annexed drawings:

FIG. I is a longitudinal vertical section of the subject burner;

FIG. 2 is a similar sectional view of said burner as installed in a refractory-lined casing within a large industrial type furnace; and

FIG. 3 is an enlarged sectional view of the atomizer tip end shown in FIG. 1.

DESCRIPTION OF THE INVENTION Referring now to the attached drawings, which illustrate a preferred embodiment of this invention, the burner is shown as mounted within a refractory-lined outer metal casing ll. Said casing 11 has a top air inlet 12 and forward outlet holes 13 in a forward air-distributing member 13' for supplying and uniformly distributing combustion air to the front of the burner 10. Said burner 10 pro'ects through the on 14 in the inner refractory wall of a metallurgical heating umace 15 has an end portion 17 comprising an intumed annular flange 17' and a central discharge opening 17" in the outer end thereof. An axially disposed oil nozzle 18 extends centrally within said first gaseous fuel tube 16. Said nozzle 18 has a plurality of radial outlet ducts l9, and its outer face 20 defines a constricted discharge passage 21 with said primary gaseous fuel tube opening 17. Oil is introduced through a liquid fuel tube 22 communicating with said nozzle 18, and is injected through the ducts 19 into the primary gas stream for atomiza tion.

In order to meet a specified maximum gas flow of the order of 4,300 s.c.f.h., the gas capacity of this burner has been increased by the provision of a secondary gaseous fuel tube 23 surrounding the primary gaseous fuel tube 16 and supplying the secondary portion of gas fired by the burner. Said secondary gas discharges from the secondary gaseous fuel tube 23 through a constricted intumed circular flange or annulus 24 and impinges on the gas-oil mixture discharging through said passage 21 and from primary gaseous fuel tube opening 17.

Liquid fuel is supplied to the liquid fuel tube 22 by means of the liquid fuel inlet line 25. A single gas inlet line 26 is provided with a T-fitting 27 from which emerges one gas line 28 which supplies primary gas to the primary gaseous fuel tube 16, and a second gas line 29 which supplies secondary gas to the secondary gaseous fuel tube 23.

A back-pressure gas regulator valve 30 is inserted in said second gas line 29 so as to maintain constant the pressure of the primary gas flowing to the atomizer nozzle 18, with the remainder of the gas going to the annulus 24 acting as a secondary gas nozzle. The pressure regulator valve 30 may then be adjusted, for instance, to maintain 40 p.s.i.g. as the primary gas pressure over the range of total gas flow rates of 720 to 4,300 s.c.f.h.

In the specific embodiment of the invention as described, the outer diameter of the liquid fuel nozzle 18 is is inch, and the diameter of each of the ducts 19 therein as about 3/32 inch. The inner diameter of the primary gas tube 16 is 1% inches, and that of the secondary gas tube 23 is 2 /4 inches. Oil pressure is maintained at about 45 to 55 p.s.i.g., and the primary gas pressure is kept at approximately 40 p.s.i.g. as stated. Gas in excess of 720 s.c.f.h. serves as secondary gas.

While the foregoing description of the invention refers only to a single burner, it will be understood that this invention is adaptable to use with a plurality of burners when all are firing concurrently and at the same rate in a large furnace.

We claim:

1. In combination with a liquid/gaseous fuel burner including a primary gaseous fuel tube having an opening in the outer end thereof, a nozzle extending within said primary gaseous fuel tube, the outer portion of said nozzle defining a gaseous discharge passage with said gaseous fuel tube opening, orifice means in said nozzle communicating with said discharge passage, a liquid fuel tube communicating with said nozzle, a secondary gaseous fuel tube communicating with said opening, means to supply liquid fuel to said liquid fuel tube, means to supply gaseous fuel to said primary gaseous fuel tube, and additional means to supply gaseous fuel to said secondary gaseous fuel tube, the improvement comprising:

a. pressure-regulating means responsive to the gas pressure in said primary gaseous fuel supply as a means to maintain substantially constant the pressure of gaseous fuel passing through said primary gaseous fuel tube and said nozzle by regulating the flow of gaseous fuel passing through said secondary gaseous fuel tube. 

